A synapse is formed _______________________________________ a gap called synaptic cleft.

( A ) by the membranes of a post-synaptic neuron and a post-synaptic axon, which is not be separated by
( B ) by the membranes of a pre-synaptic axon and a pre-synaptic neuron, which is separated by
( C ) by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which is not separated by
( D ) by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by